1. Field of the Invention
The present invention relates to a quartz crystal device having a configuration in which a quartz crystal unit and an IC (integrated circuit) chip including a circuit using the crystal unit are integrated, and particularly relates to a quartz crystal device provided with a monitor electrode for inspecting characteristics of a crystal blank used in the crystal element from outside.
2. Description of the Related Art
As a typical quartz crystal device in which a quartz crystal unit and an IC chip are integrated, there is a surface-mount oscillator in which a crystal unit and an IC chip on which an oscillating circuit using the crystal unit are integrated. Surface-mount crystal oscillators are widely incorporated especially in portable electronic apparatuses such as portable telephones, for example, as reference sources for frequency and time because of their compactness and light weight.
As one type of such a surface-mount crystal oscillator, there is a bonding type surface-mount crystal oscillator in which an IC chip and a quartz crystal blank are respectively housed in separate containers and thereafter, the containers are joined to be integrated, as disclosed in Japanese Patent Laid-Open No. 2004-88533 (JP-A-2004-088533). FIG. 1A is a side view showing one example of a configuration of a conventional bonding type surface-mount crystal oscillator. FIG. 1B is an assembled sectional view of the crystal oscillator. FIGS. 2A and 2B are respectively a top view and a bottom view of a mounting substrate for use in the crystal oscillator. FIG. 3 is a bottom view of a crystal unit in the crystal oscillator.
The illustrated crystal oscillator includes mounting substrate 2 housing IC chip 1, and crystal unit 3 in which crystal blank 8 is hermetically encapsulated, in which mounting substrate 2 is joined to a bottom surface of crystal unit 3 Mounting substrate 2 is a planar member with a substantially rectangular plane shape, and a recess for housing IC chip 1 is formed on one of principal surfaces of mounting substrate 2.
Mounting substrate 2 is configured by laminated ceramics constituted of planar bottom wall layer 2a in a substantially rectangular shape, and frame wall layer 2b provided on bottom wall layer 2a in a frame shape, and a side wall of the recess of mounting substrate 2 is formed by frame wall layer 2. At four corner portions on a top surface of frame wall layer 2b, that is, the four corner portions of an opening end surface surrounding the recess of mounting substrate 2, bonding terminals 5 for electrically and mechanically joining mounting substrate 2 to the bottom surface of crystal unit 3 are formed. Mounting terminals 4 which are used when the crystal oscillator is surface-mounted on a wiring board are provided at four corner portions of an undersurface illustrated in the drawing of bottom wall layer 2a, that is, an outer bottom surface of mounting substrate 2.
IC chip 1 has a substantially rectangular shape, in which electronic circuits including at least an oscillating circuit using crystal unit 3 are integrated on a semiconductor substrate. In IC chip 1, the electronic circuits such as the oscillating circuit are formed on one principal surface of the semiconductor substrate by an ordinary semiconductor device fabricating process, and therefore, of a pair of principal surfaces of the semiconductor substrate, the principal surface on which the electronic circuits are formed will be called a circuit formation surface of the IC chip. A plurality of IC terminals for connecting IC chip 1 to an external circuit are also formed on the circuit formation surface. The IC terminals include a power supply terminal, a ground terminal, an oscillation output terminal, an AFC (automatic frequency control) terminal, a pair of crystal connection terminals for connecting to the crystal oscillator, and the like.
Circuit terminals 11 are provided on a bottom surface of the recess of mounting substrate 2, that is, an exposure surface of bottom wall layer 2a by the recess to correspond to the IC terminals. The circuit terminals corresponding to the IC terminals, which are the power supply terminal, the ground terminal, the oscillation output terminal and the AFC terminal, are electrically connected to mounting terminals 4 respectively through conductive paths (not shown) formed in mounting substrate 2. The circuit terminals corresponding to a pair of crystal connection terminals of IC chip 2 are electrically connected to bonding terminals 5(X) at both ends of one diagonal line of mounting substrate 2, for example, through conductive paths (not shown). Remaining two bonding terminals 5(GND) are electrically connected to ground terminals 4(GND) out of mounting terminals 4 via through-holes provided in mounting substrate 2, for example.
IC chip 1 is fixed to the inner bottom surface of the recess of mounting substrate 2 by causing the circuit formation surface to face the inner bottom surface of the recess of mounting substrate 2, and electrically and mechanically connecting the IC terminals to circuit terminals 11 by ultrasonic thermo-compression bonding using bumps 6. In order to protect the circuit formation surface of IC chip 1, protection resin layer 16 is provided in the recess of mounting substrate 2 as so-called underfill so as to bury a space between the inner bottom surface of the recess and the circuit formation surface.
Meanwhile, crystal unit 3 is such that crystal blank 8 is hermetically encapsulated in a recess of container body 7 by housing crystal blank 8 in container body 7, and joining metal cover 9 to an opening end surface surrounding the recess. Container body 7 is constituted of laminated ceramics having the recess. In the illustrated one, metal cover 9 is joined to a metal thick film or metal ring 15 provided at the opening end surface by seam welding or beam welding. External terminals 10 corresponding to bonding terminals 5 of mounting substrate 2 are provided at four corner portions of an outer bottom surface of container body 7. A pair of crystal holding terminals 12 for holding crystal blank 8 are provided on an inner bottom surface of the recess of container body 7.
Crystal blank 8 is, for example, a substantially rectangular AT-cut quartz crystal blank, in which excitation electrodes (not shown) are respectively provided on both of its principal surfaces, and from the excitation electrodes, lead electrodes (not shown) are extended to both sides of one end portion of crystal blank 8. By fixing both the sides of the one end portion of crystal blank 8 where the lead electrodes are extended with conductive adhesive 13 or the like to crystal holding terminals 12, crystal blank 8 is electrically and mechanically connected to crystal holding terminals 12, and held in the recess of container body 7.
In container body 7, a pair of crystal holding terminals 12 are electrically connected to a pair of external terminals 10(X) on one diagonal line in the outer bottom surface of container body 7 through conductive paths (not shown) formed in container body 7. External terminals 10(GND) on the other diagonal line in the outer bottom surface are electrically connected to metal cover 9 through via holes provided in container body 7.
By connecting bonding terminals 5 of mounting substrate 2 to external terminals 10 of crystal unit 3 by using solder or the like, mounting substrate 2 and crystal unit 3 are electrically and mechanically connected, and are completed as a surface-mounting crystal oscillator. At this time, crystal holding terminals 12 in crystal unit 3 are electrically connected to the IC terminals through external terminals 10(X), bonding terminals 5(X) and circuit terminals 11, and therefore, crystal blank 8 is electrically connected to the oscillating circuit in IC chip 1. Metal cover 9 is also electrically connected to ground terminal 4(GND) of the mounting terminals.
Such a bonding type surface-mount crystal oscillator is ultimately assembled by independently forming mounting substrate 2 loaded with IC chip 1 and crystal unit 3, and thereafter, joining both of them. On this occasion, before mounting substrate 2 is joined to the outer bottom surface of crystal unit 3, probes of a measuring apparatus are caused to abut on a pair of external terminals 10(X), which are formed on the outer bottom surface of container body 7 of crystal unit 3 and electrically connected to crystal blank 8, to measure a vibration characteristic and the like of crystal blank 8, and whether crystal unit 3 is good or not is determined. As the vibration characteristic, crystal impedance (CI) is generally measured. Here, when it is determined as a defective, crystal unit 3 is removed from the manufacturing process, and mounting substrate 2 is joined to only good crystal unit 3. Thereby, an expensive IC chip is not wasted, and productivity can be enhanced. Further, external terminals 10(X) are formed within the same plane, and probes can be caused to abut on a pair of external terminals 10(X) form one direction. Therefore, the operation efficiency of measurement of the vibration characteristic becomes high.
As another type of a surface-mount crystal oscillator, there is a so-called. two-chamber type in which by using a container body with recesses formed respectively on both principal surfaces, a crystal blank is hermetically encapsulated in the recess of one principal surface to configure a crystal unit, and an IC chip is accommodated in the recess on the other principal surface. A two-chamber type surface-mount crystal oscillator is also called an H-shaped surface-mount crystal oscillator since a container body in which the sectional shape in a central portion is in a H-shape is used. FIG. 4A is a side view of such a two-chamber type surface-mount crystal oscillator. FIG. 4B is a sectional view of it. FIG. 5 is a bottom view of the container body with an IC chip removed. In these drawings, the same components as those in FIGS. 1A, 1B, 2A, 2B and 3 are assigned with the same reference numerals, and the redundant description of them will be omitted or simplified.
Container body 21 has a flat outer shape in a substantially rectangular parallelepiped shape which looks like a rectangle having short sides and long sides seen from above when mounted on a wiring board, and are provided with recesses on its top surface and undersurface respectively. As a result, container body 21 has an H-shaped sectional shape. Container body 21 is constituted of laminated ceramics having planar central layer 21a in a substantially rectangular shape, and upper and lower frame layers 21b and 21c respectively having rectangular openings. First recess 20a at an upper side illustrated in the drawing is formed by central layer 21a and frame layer 21b, and quartz crystal blank 8 which functions as a crystal unit is encapsulated in first recess 20a. Further, second recess 20b at a lower side illustrated in the drawing is formed by central layer 21a and frame layer 21c, and IC chip 1 is housed in second recess 20b. 
A pair of crystal holding terminals 12 are provided on an inner bottom surface of first recess 20a, that is, a surface of a front side of central layer 21a, and crystal blank 8 is fixed and held in first recess 20a by fixing lead electrodes to crystal holding terminals 12 with, for example, conductive adhesive 13 or the like at the positions where the pair of lead electrodes are led out, as in the case shown in FIGS. 1A and 1B. After fixing crystal blank 8, in the opening end surface of first recess 20a of container body 21, metal cover 9 is joined to metal ring 15 provided on a top surface of frame layer 21b by seam welding or the like, whereby crystal blank 8 is hermetically encapsulated in first recess 20a 
In container body 21, mounting terminals 4 which are used when the crystal oscillator is surface-mounted on a wiring board are respectively formed at four corner portions of the opening end surface of frame layer 21c forming second recess 20b. Further, on an inner bottom surface of second recess 20b, that is, a back surface of central layer 21a, a plurality of circuit terminals 11 are disposed to be along both long sides of central layer 21a as shown in FIG. 5. As in the above-described case, circuit terminals 11 are provided to correspond to IC terminals provided on IC chip 1. In the illustrated example, four circuit terminals 11 are provided in a line along each long side. Four of circuit terminals 11 correspond to, for example, a power source terminal, a ground terminal, an oscillation output terminal, and AFC terminal of the IC terminals, and are electrically connected to corresponding mounting terminals 4 by conductive paths (not shown) formed in central layer 21a. Further, two of remaining circuit terminals 11 are crystal circuit terminals 11a electrically connected to crystal blank 8. Crystal circuit terminals 11a are electrically connected to crystal holding terminals 12 provided on the inner bottom surface of first recess 20a through conductive paths (not shown) such as via holes provided in central layer 21a. Further, a pair of crystal inspection terminals X1, X2 are provided on the back surface of central layer 21a. Crystal inspection terminals X1, X2 are electrically connected to crystal circuit terminals 11a by a conductive pattern provided on the back surface of central layer 21a. Accordingly, crystal inspection terminals X1, X2 are electrically connected to crystal blank 8.
As IC chip 1, the one as described above is used. IC chip 1 is fixed to the bottom surface of second recess 20b by joining the IC terminals to circuit terminals 11, 11a provided on the bottom surface of second recess 20b by ultrasonic thermo-compression bonding using bumps 6 by the method of so-called flip chip bonding.
When such a two-chamber type surface-mount crystal oscillator is manufactured, first, a crystal unit is configured by hermetically encapsulating crystal blank 8 in first recess 20a, and thereafter, probes for measurement are caused to abut on crystal inspection terminals X1, X2 which are provided on the bottom surface of second recess 20b, that is, the back surface of central layer 21a, whereby the vibration characteristic or the like of crystal blank 8 as a crystal unit is measured. At this time, the probes can be caused to abut on a pair of crystal inspection terminals X1, X2 from one direction, and operation efficiency of measurement of the vibration characteristic or the like becomes high. The crystal unit which has abnormality in the vibration characteristic or the like is discarded as a defective, and for the one which is determined as good, IC chip 1 is subsequently mounted on the bottom surface of second recess 20b. Protective resin layer 16 as underfill for protecting a circuit formation surface of IC chip 1 is further provided, and thereby, a crystal oscillator is completed. Japanese Patent Laid-Open No. 2000-49560 (JP-A-2000-49560), for example, describes disposing crystal inspection terminals on the bottom surface of the recess where the IC chip is to be mounted in the container body, and fixing the IC chip to the bottom surface of the recess after measurement of the oscillation characteristic or the like of the crystal blank in a two-chamber type crystal oscillator.
As a surface-mount crystal oscillator, there is a one-chamber type crystal oscillator in which by using a container body having one recess with a step portion formed on an inner wall, an IC chip is fixed to an inner bottom surface of the recess, and both sides of one end portion of a crystal blank where lead electrodes are extended are fixed to the step portion, whereby the crystal blank is disposed above the IC chip. In the one-chamber type crystal oscillator, the crystal blank is fixed after the IC chip is mounted on the bottom surface of the recess. Therefore, the IC chip cannot be mounted after measurement of the vibration characteristic of the crystal blank. The vibration characteristic is measured after the IC chip is mounted and the crystal blank is fixed.
Japanese Patent Laid-Open No. 2003-298000 (JP-A-2003-298000) discloses to form the terminals to be used for measurement of the vibration characteristic of a crystal blank, that is, the crystal inspection terminals, on an outer surface of the container body in a one-chamber type crystal oscillator.
In the above described bonding type surface-mount crystal oscillator, after the mounting substrate is joined to the crystal unit, external terminals 10(X) electrically connected to crystal blank 8 are not exposed to an outside, and therefore, the vibration characteristic of crystal blank 8 cannot be measured individually. Similarly, in the two-chamber type surface-mount crystal oscillator, after the IC chip is mounted, crystal inspection terminals X1, X2 are hidden by the IC chip, and therefore, the vibration characteristic of crystal blank 8 cannot be individually measured. However, in order to enhance reliability of the crystal oscillator and respond to request for high functionality, it is required to be able to measure the vibration characteristic of crystal blank 8 even after mounting substrate 2 loaded with IC chip 1 is joined to the bottom surface of crystal unit 3 in the case of a bonding type, or even after IC chip 1 is mounted on the bottom surface of the recess of container body 21 in the case of two-chamber type. More specifically, it is required to be able to measure the vibration characteristic of the crystal blank without passing through the IC chip when whether a product is good or bad is finally determined before shipment after completion of a crystal oscillator, and when failure analysis is performed for searching the cause of a trouble when the trouble occurs during use of a crystal oscillator.